Graphical user-interfaces have permitted a significant number of users who are not familiar with the nuances involved in specifying geometric objects using a specification language to graphically enter such objects into a digital device such as a computer, calculator, personal digital assistant, etc. Using a stylus, mouse, or cursor keys, a user can draw a geometric object, such as a polygon, and have the object be entered into the digital device just as if the user had used a formal specification language to create the object.
After entering the object into the digital device, the user can use the digital device to determine information about the object such as the objects' dimensions, surface area, angles, arc lengths, and other physical properties. Such a device can be helpful in teaching people about geometric shapes and their properties.
However, by allowing freeform entry via a user interface, the system may be prone to errors. A user may not draw the object correctly and as a result, the digital device may not be able to calculate the properties of the object or worse, the digital device may inaccurately calculate the properties of the object. Because of the fact that the users of such devices tend to be novices or students, incorrect answers can rapidly erode their confidence in using the digital device.
A need has therefore arisen for a system that will detect an invalid polygonal object and notify the user that the object he has just drawn is invalid without complex error detection algorithms.